This invention relates in general to xerography and more specifically to a novel photosensitive device.
Vitreous and amorphous selenium is a photoconductive material which has had wide use as a reusable photoconductor in commercial xerography. However, its spectral response is limited largely to the blue-green portion of the visible spectrum, i.e. below 5200 angstrom units.
Selenium also exists in a crystalline form known as trigonal or hexagonal selenium. Trigonal selenium is well known in the semiconductor art for use in the manufacture of selenium rectifiers.
In the past, trigonal selenium was not normally used in xerography as a photoconductive layer because of its relatively high electrical conductivity in the dark, although in some instances, trigonal selenium can be used in a binder configuration in which the trigonal selenium particles are dispersed in the matrix of another material such as an electrically active organic material such as vitreous selenium.
It is also known that a thin layer of trigonal selenium overcoated with a relatively thick layer of electrically active organic material, forms a useful composite photosensitive member which exhibits improved spectral response and increased sensitivity over conventional vitreous selenium-type photoreceptors. This device and method are described in U.S. Pat. No. 3,961,953 to Millonzi et al.
It is known that when using trigonal selenium whether it be dispersed in a binder or used as a generation material in a composite photoconductive device that the trigonal selenium exhibits a high dark decay and high dark decay after the photoreceptor has been cycled in a xerographic process. This is referred to as fatigue dark decay. Also, after cycling the photoreceptor in a xerographic process, the photoreceptor will not accept as much charge as it did initially.